Dynamic-coupling analyses of cells localization by the negative dielectrophoresis

Negative dielectrophoresis is widely used in cell localization for long-term observations such as the impedance analysis, in vivo drug screening, and cell patterns. However, the coupling effect of AC electrokinetics, including negative dielectrophoresis, AC electroosmosis, and electrothermal flow is still unclear. This work investigated cell localization based on the dynamic-coupling of dielectrophoresis, AC electroosmosis, and electrothermal flow. A two-dimensional finite element model that consisted of interdigitated array electrodes was established. The effects of system parameters on the capture efficiency were investigated, when the medium conductivity was in the range of 0.001–1 S/m. The selection of the medium conductivity is suggested to be the first step of the experiment design. Then, the choice of AC frequency and AC amplitude requires balancing the effects of transmembrane potential and temperature rise on cell viability. Besides, particular electrode spacing is evidenced to be only efficient for a specific cell diameter. Thus, the electrode spacing of the microfluidic chip needs to be optimized according to the cell's diameter.

Application of genetic algorithm in extracting cell dielectric characteristics with electrorotation

In this study the transformed theory is applied to derive the dielectric characteristics of cells, considering the electrorotation (ER) peak frequency. In current studies, estimations of low frequency, which are credible for the values less than 1 mS/m for medium conductivity, are used to obtain the corresponding permittivity and conductivity of cells. Unlike the presented works, the transformed theory applies the comprehensive statement for corresponding permittivity and conductivity of cells. In the transformed theory, the membrane and interior characteristics could be obtained from the high and the low frequencies of peak ER, for all values of conductivity of medium. Characteristics of cells are obtained via optimization of an equation for the conductivity of medium regarding the peak ER frequency. The optimization process is performed applying genetic algorithm due to its swift adaptation to the problem and faster convergence.

Three new Fragilaria species (Bacillariophyta) from low-conductivity mountain freshwaters (Alps and Apennines)

More or less needle-shaped species of Fragilaria s.s. are difficult to identify. Here we contribute to the taxonomy of this difficult group by describing three species new to science from very low conductivity mountain freshwater environments. Two of the new species resemble taxa established by Kützing in the early 19th century: F. rumpens and F. vaucheriae. Fragilaria spinaspeciosa sp. nov., from a seepage (helocrenic spring) in the northern Apennines, is superficially similar to F. rumpens, but has a lower stria density. Fragilaria tridentina sp. nov. is distinguished from F. gracilis by its smaller length-to-breadth ratio and more closely spaced areolae. Fragilaria vaucheriaeraetica sp. nov. is distinguished from F. vaucheriae and F. microvaucheriae by its outline and denser striae. These last three species also have distinctly different ecologies. Fragilaria vaucheriaeraetica sp. nov. is found in very low conductivity, very low nitrate, ultra-oligotrophic waters, while F. vaucheriae and F. microvaucheriae are found in medium conductivity, high total phosphorus, and relatively high nitrate streams. Accurate species identification and knowledge of each species’ ecological preferences are critically important if diatoms are to be used effectively as indicators of environmental impact and climate change. Weakly buffered, low alkalinity, low nutrient and low conductivity mountain freshwater habitats are sensitive to human disturbance and biotopes for many rare (Red List) diatoms. As such, they serve as valuable early warning systems for detecting the effects of climate change and other human activities.

Gomphonema Vibrio Var. Subcapitatum (Bacillariophyceae), New for Poland

Gomphonema vibrio var. subcapitatum (A. Mayer) J. H. Lee, hitherto unknown in Poland, is reported here from six lakes in the northeastern part of the country. This diatom prefers alkaline waters of medium conductivity and low nitrate and chlorine concentrations. The taxon is documented by SEM images and LM micrographs, and its morphological variability and distribution are briefly discussed.